Rounded corners and shading issues
One method:

Add a Plane and scale on the "X" axis to form your rectangle. 



TAB into Edit Mode and add four Loop Cuts (CTRL + R) positioned where you want your hole to be.



Select all by pressing "A". Extrude by pressing "E" + "Z" to constrain on the z axis.



Scale in by pressing "S" + SHIFT "Z" to constrain to the x and y axis.

Select the inner top face and press "X" and "Only Faces" from the drop down menu to delete it.



Add a Subdivision Surface Modifier (View and Render set to two.



Tab into Object Mode and set shading to Smooth. Tab back into Edit Mode and add Loop cuts to tighten up you corners.



Repeat for all your corners.